1. Field of the Invention
The present invention relates to a multi-functional hybrid contactor, and more particularly, to a multi-functional hybrid contactor having a function of an electronic motor protection relay (EMPR) and a function of selectively starting a motor in a direct starting mode or a soft starting mode.
2. Description of the Background Art
In general, a method for starting a motor includes a direct starting method for supplying a power source voltage directly to a motor by using a relay and a relay contact and a soft starting method using a semiconductor switch device.
The direct starting method has a problem that, since the power source voltage is directly supplied to the motor, much surge current is caused on power supplying to damage a motor and a contact of a contactor is also damaged.
In order to protect the motor against the surge current generated in starting a motor for improving the direct starting method, a method has been proposed in which a motor is started by a so-called xe2x80x98star connectionxe2x80x99 in its starting and the star connection is converted into a so-called xe2x80x98delta connectionxe2x80x99 to operate the motor in an operation that a stable power source voltage is supplied, as shown in FIG. 1.
FIG. 1 illustrates a motor control apparatus adopting the prior art.
As shown in FIG. 1, a motor control apparatus includes: a circuit breaker (MCCB: Molded case circuit breaker) 11 for conducting or cutting off a source current inputted from a three-phase power source terminal (R, S, T); an electronic motor protection relay (EMPR) 14 for monitoring an inverted phase, a phase deficiency, an unbalance of phases, an overload or an over current during an operation of a motor 16 so as to determine whether there is an error in the source current supplied to the motor 16 and protect the motor 16; a power supply contactor (MCM) 15 for switching-controlling the three-phase current applied to the motor 16 through coils U, V and W of the motor 16 from the electronic motor protection relay 14; and an operation contactor (MCD) 17 for switching-controlling the current applied to the motor 16 through coils X, Y and Z of the motor 16 from the electronic motor protection relay 14; a starting contactor (MCS) 18 being connected to the coils X, Y and Z of the motor 16 and turned on in starting; and an auxiliary circuit 13 being connected to the three contactors 15, 17 and 18 and sequence-controlling ON/OFF of the contactors 15, 17 and 18.
The operation of the motor control apparatus constructed as described above will now be described.
First, in a state that three-phase alternating current (abbreviated AC hereinafter) is being supplied as three contacts of the molded case circuit breaker 11 are closed, when a user presses a starting switch 12 connected to the auxiliary circuit 13 in order to operate the motor 16, the electronic motor protection relay 14 supplies three-phase power current, and at the same time, starts to continuously monitor the current being supplied to a circuit of the motor 16.
At this time, the auxiliary circuit 13 magnetizes a power supplying contactor controlling relay (not shown) and a starting contactor controlling relay (not shown) installed therein to close the power supplying contactor and the starting contactor 18, and accordingly, the motor 16 assumes a so-called xe2x80x98star connectionxe2x80x99 (i.e., xe2x80x98Y connectionxe2x80x99) configuration and starts rotating.
Subsequently, when a predetermined time elapses after the motor 16 is started, the auxiliary circuit stops the magnetization of the starting contactor controlling relay to open (OFF) the starting contactor 18 and magnetize an operating contactor controlling relay to close the operation contactor 17.
Then, as the connection configuration of the motor 16 is changed to a so-called xe2x80x98delta connectionxe2x80x99, a rated voltage is supplied to the motor 16.
Meanwhile, when the motor 16 starts rotating and a current flows, the electronic motor 16 protection relay 14 continuously measures the current flowing to the motor in order to determine whether there occurs an error in the power current.
If an error is detected from the power current, a cut-off signal is transmitted from the motor protection relay 14, passing the auxiliary circuit 13, to the power supplying contactor 15, so that the power supply contactor 15 is opened to cut off the power being supplied to the motor 16.
However, though the conventional motor control apparatus having the so-called star/delta connection"" configuration converting method advantageously reduces the surge current, it fails to have a complete soft starting characteristic. In addition, in order to reduce the surge current, three contactors, one timer for switching starting and operating and three contactor controlling relay are required only to complicate its structure and enlarge its volume.
Moreover, in case that the motor is frequently opened and closed, the contact of the contactor and the motor may be damaged due to an arc generated at the contact of the contactor.
Furthermore, the conventional motor control apparatus can not be applied to a motor which has no function of converting to the xe2x80x98star-delta connectionxe2x80x99.
That is, in general, in case of a motor having a rated voltage of 3-phase 380V or 440V, if a rated voltage is 220V, the motor is operated in a delta connection configuration, while if a rated voltage is 380V or 440V, the motor is operated in a star connection configuration.
Accordingly, in case that a rated voltage of the motor is 220V, the star-delta soft starting method can be adopted. But, in case that a rated voltage is 380V or 440V, since the xe2x80x98star connectionxe2x80x99 itself is a condition for applying a rated voltage to the coil of a motor, an appropriate motor needs to be specially manufactured in order to apply the star-delta connection method.
As one solution to the problems, a solid-state switched soft starter (SSSS) method for controlling a level of a voltage applied to a motor or a variable voltage variable frequency (VVVF) method for converting a voltage by a frequency is used.
However, such equipment is more expensive compared to the apparatus operated in a star-delta connection method, and there are difficulties in its application.
In addition, as for the SSSS constructed with only semiconductor switches, during current conducting, heat is generated due to a loss at the both ends of a switch and thus a large heat sink is required to cool the heat, resulting in an increased size of the motor control apparatus.
FIG. 2 is a schematic block diagram of a hybrid contactor in accordance with the prior art.
As shown in FIG. 2, a soft starting type motor control apparatus using a hybrid contactor to prevent an arc current generated at the instant when a mechanical relay contact is turned off, including: a main contact 40 of a contactor connected between an AC power source 30 and a load (motor) 60; a relay 50 for controlling switching of the main contact 40 of the contactor; a switch unit 23 having silicon controlled rectifiers (SCR1 and SCR2), that is, semiconductor switching devices, connected in parallel in an inverse direction at the main contact 40 and turned on at a time just before and at a time just after the main contact 40 is closed in order to supply a load current; a snubber 22 for restricting a spike voltage generated at both ends of the switch unit to be below a predetermined value; a driving coil voltage controller 80 for outputting a coil driving voltage (V_coil) to the relay 50, detecting a level change of an input driving voltage (V-input), and outputting a gate driving pulse stream (Vx); and gate driving units 21 and 70 being driven by the gate driving pulse stream (Vx) and supplying a drive signal to the switching unit.
The snubber 22 includes a resistance R3, a condenser C3 and a varistor (ZNR1) restraining an over current.
FIG. 3 is a detailed block diagram of the driving coil voltage controller of FIG. 2.
As shown in FIG. 3, the driving coil voltage controller includes: a rectifying circuit 81 for converting an AC input voltage (V_input) to a direct current and outputting the direct current so that no matter what type of AC or DC a driving coil driving voltage inputted from an external source is applied thereto; a constant voltage generating circuit 83 for receiving a DC voltage from the rectifying circuit 81 and generating a control voltage (Vcc) and a drive voltage (Vdd); a voltage dividing circuit 82 for dividing the DC voltage inputted from the rectifying circuit 81 to a predetermined level; a voltage detecting circuit 84 for generating a high level signal if voltages inputted from the voltage dividing circuit 82 and the constant voltage generating circuit 83 are higher than a predetermined value, and generating a low level signal if voltages inputted from the voltage dividing circuit 82 and the constant voltage generating circuit 83 are lower than a predetermined value; a pulse generating circuit 85 for generating short pulses (Tp, Ta, Te and Td) by a signal outputted from the voltage detecting circuit 84; a pulse width controller 87 for determining a DC value so that an optimum coil drive voltage (V_coil) can be shown according to the size of the driving input voltage (V_input), an operation temperature, and an amount of current passing through the driving coil; an oscillator and triangle wave generator 86 for generating a triangle wave signal according to an inputted voltage; and a comparator for generating a pulse width modulation wave form (S_PWM) signal by a signal inputted from the pulse width controller 87 and the oscillator and triangle wave generator 86.
The operation of the hybrid contactor constructed as described above will now be explained with reference to FIG. 4.
FIG. 4 is a drawing showing wave forms according to operations of FIGS. 2 and 3.
First, when the input voltage (V_input) is applied to the driving coil voltage controller 80 at an arbitrary time point t0, the rectifying circuit 81 of the driving coil voltage controller 80 rectifies the input voltage to a DC voltage and outputs the DC voltage to the voltage dividing circuit 82 and the constant voltage generating circuit 83.
The voltage dividing circuit 82 divides the inputted DC voltage to a certain level, and the constant voltage generating circuit 83 generates a control voltage (Vcc) and a drive voltage (Vdd) using the inputted DC voltage.
The voltage detecting circuit 84 detects a level change of the input driving voltage (V_input) on the basis of the output voltage of the voltage dividing circuit 82 and the output voltage (Vcc) of the constant voltage generating circuit 83, and outputs a high level detect signal (V_com) if the input drive voltage (V_input) increases above a predetermined level, and outputs a low level detect signal if the input drive voltage decreases below a predetermined level.
That is, as shown in FIG. 4B, the level detect signal (V_com) of the voltage detecting circuit 84 is changed from a low level to a high level at a time point (t1) upon the lapse of a certain time.
When the level detect signal (V_com) outputted from the voltage detecting circuit 84 is inputted to the pulse generating circuit 85, a first pulse generator 85-1 of the pulse generating circuit 85 generates a pulse having a pulse width of Tp to generate a coil drive voltage (V_Coil) (as shown in FIG. 4C), while a second pulse generator 85-2 generates a one-period pulse (V_pulse) having a pulse width of Ta (as shown in FIG. 4D).
Subsequently, for the time interval [t1xe2x88x92t2], the main contact 40 of the contactor is not closed and it is in a state that an operable contact part is being closed.
In general, in order to close the main contact 40 of the contactor, time of about Tb (20xcx9c50 ms) as shown in FIG. 4E is required, for which, thus, the driving coil voltage controller 80 may output the coil drive voltage (V_coil) to the relay 50 and supply a drive signal to gates G1 and G2 of the SCR1 and SCR2 of the switching circuit 23. At this time, Ta becomes xe2x80x980xe2x80x99 and a pulse generating circuit is not necessary.
However, in order to minimize the amount of heat from SCR1 and SCR2, a pulse generator 85-4 delays a turn-on operation of the SCR1 and SCR2 for a certain time (Ta=about 2 ms), and generates a pulse having a pulse width of Td as shown in FIG. 4F at an instant when its own output pulse (V_pulse) is changed from a high level to a low level.
The pulse outputted from the pulse generator passes an OR gate (OR82) and is inputted to an AND gate AD82. Then, the AND gate AD82 ANDs the ORed pulse and a pulse width modulation signal (S_Pwm) of a comparator 89, and outputs a gate drive pulse stream (Vx) (refer to FIG. 4G).
A gate driving circuit 70 is driven by the gate drive pulse stream (Vx) outputted from the AND gate AD82, and the SCR1 and SCR2 are turned on by the drive signals of the gate (G1 and G2) generated from the gate driving circuit 70.
For example, when the main contact 40 is closed at a time point t3, the SCR1 and SCR2 are turned on at a time point t2, so that a current is supplied to the load 60 through the SCR1 and SCR2 as shown in FIG. 4H. And at an instant when the main contact 40 is open, the both end voltage of the SCR1 and SCR2 becomes zero and the SCR1 and SCR2 are turned off.
Even if the main contact 40 of the contactor is not completely closed at the time point t3 and a chattering occurs, as shown in FIG. 4G, since the SCR1 and SCR2 are repeatedly turned on and off by the gate drive pulse stream (Vx) supplied to the gates G1 and G2 of the SCR1 and SCR2 connected in parallel to the main contact 40 up to an arbitrary time point t4, so that an arc current is consumed by the SCR1 and SCR2 at the main contact 40 of the contactor.
By the above described process, if a high voltage is continuously supplied to the drive coil 50 even after completion of the turn-on operation of the contactor, the drive coil 50 may be damaged or a strong residual magnet component may be caused. Thus, a coil drive voltage (V_coil) having a pulse width in a modulated form as shown in FIG. 4C is supplied.
At this time, the pulse width is sufficient even if it is short, e.g., having a width of only a few microseconds, and in this respect, in order to reduce an audible noise, it is necessary to use a frequency of about 20 kHz.
For this purpose, the comparator 89 compares the output pulse of the oscillator and triangle wave generator 86 and the output pulse of the pulse width controller 87 to generate a pulse width modulation signal (S_PWM) and supplies the pulse width modulation signal (S_PWM) to one input terminal of the AND gate AD81.
Accordingly, as shown in FIGS. 4B and 4C, the requested pulse stream can be supplied through a coil driving circuit 88 for an interval where the detect voltage (V_com) of the voltage detecting circuit 84 is high.
Meanwhile, when the input drive voltage (V_input) starts to be changed from a high level to a low level, a level detect signal (V_Com) of the voltage detecting circuit 84 is changed from a high level to a low level at an arbitrary time point t5 (as shown in FIG. 4B).
At this time, the pulse generator 85-3 generates a pulse having a pulse width of Te (as shown in FIG. 4F). The pulse passes the OR gate 82, and then, the AND gate AD82 ANDs it with the output signal of the comparator 89 and generates a gate driving pulse stream (Vx) (as shown in FIG. 4G).
When the gate driving pulse stream (Vx) is inputted to the gate driving circuit 70, the gate driving circuit 21 generates gate (G1, G2) drive signals of the SCR1 and SCR2.
However, the main contact 40 is not opened at the same time when the gate drive signal is generated and a certain delay time (Tc) is taken. Thus, the SCR1 and SCR2 are maintained in an OFF state at the corresponding delay time interval (t5xcx9ct6), and at the instant when the main contact 40 is opened, the load current is supplied.
Thereafter, when the gate (G1, G2) drive signals of the SCR1 and SCR2 are cut off at a time point t7, the SCR1 and SCR2 are maintained in an ON state until a polarity of the current flowing to them is inverted, and turned off at a time point t8.
At this time, a spike voltage generated at both ends of the SCR1 and SCR2 is restrained to below a certain value by the snubber 22.
FIG. 4I shows a conduct interval of a current finally supplied to the load 60, in which the conduct interval is from the time point t2 when the SCR1 and SCR2 are turned on to the time point t8 when the SCR1 and SCR2 are turned off.
FIG. 4H shows intervals of a current flowing to the SCR1 and SCR2 when the hybrid contactor is turned on and turned off over one time.
In order to minimize a heat amount at the SCR1 and SCR2, the length of the interval Tf and Tg should be designed to be minimum.
However, in case of adopting the above described hybrid contactor to the direct starting of the motor, the amount of current divided by the semiconductor switch (SCR) connected in parallel to the mechanical relay contact differs depending on the type of a load.
That is, since the semiconductor switch connected in parallel is first turned on before the mechanical contact is closed, when a load with a large surge current initially charged by the semiconductor switch, that is, a current of 6xcx9c10 times the rated current in the same condition as the direct starting of the motor, flows to the motor.
This will now be described with reference to FIGS. 5A and 5B.
FIGS. 5A and 5B show a load pattern of the motor of the hybrid contactor in accordance with the prior art. FIG. 5A shows a so-called xe2x80x98AC3 classxe2x80x99 durability test condition and FIG. 5B shows a so-called xe2x80x98AC 4 classxe2x80x99 durability test condition that a current of 6xcx9c10 times the rated current flows.
Accordingly, the SCR1 and SCR2 should charge the surge current flowing for the time interval t2xcx9ct3.
Since the length of the interval has a relation to a switching speed of the mechanical contact, it is not constant and is controlled with a considerable design margin.
Typically, it is controlled for 2xcx9c3 periods of 60 Hz, and a capacity of a requested semiconductor switching device is determined according to the length of the interval and an amount of the surge current.
In general, in case of a solid state controller, it allows the surge current of 10 times to flow for 0.5 seconds (about 60 Hz 3 periods), which requires a high-priced semiconductor switching device having a rated current capacity larger as much as 2xcx9c3 times of the rated current capacity, and thus a product cost Is increased.
Therefore, an object of the present invention is to provide a multi-functional hybrid contactor that is capable of selectively starting an AC motor in a direct starting mode or a soft starting mode.
Another object of the present invention is to provide a multi-functional hybrid contactor that is capable of absorbing a surge current and restraining an arc generation at an initial stage of starting in a direct starting mode.
Still another object of the present invention is to provide a multi-functional hybrid contactor that is capable of reducing a capacity and a size of a semiconductor switch by supplying a current to drive an AC motor through a mechanical relay contact in starting and running and supplying a current to drive the AC motor through a semiconductor switch only on starting and stopping.
Yet another object of the present invention is to provide a multi-functional hybrid contactor that is capable of protecting a motor when an abnormal current such as an over current, a phase inversion, an phase deficiency or an unbalance of phases occurs besides a run/stop control and capable of display and/or warning such an abnormal current occurrence state.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a multi-functional contactor including: a detecting means for detecting each phase current supplied from an AC power source to an AC motor; a relay contact being installed between the AC power source and the AC motor and being able to be switched to an opened position or a closed position to supply or cut off a power from the AC power source to the AC motor; a relay for controlling switching of the relay contact; a starting mode selection switch means for selectively starting the AC motor in a direct starting mode or a soft starting mode; a semiconductor switch means being connected in parallel to the relay contact, consuming an arc current due to a chattering of the relay contact by closing for a predetermined time after switching to the closed position of the relay contact if the selection switch means is selected in a direct starting mode, and soft-starting the AC motor by turning on and off for a predetermined time before the relay contact is closed, if the selection switch means is selected in a soft-starting mode; a display means for displaying a running state of the AC motor and/or an abnormal state of an AC current supplied to the AC motor; a setting means for setting a rated current, setting a delay time for neglecting an over current during a predetermined time when the AC motor is directly started, and setting a starting time when the AC motor is soft-started; a run/stop switch means for selectively running and stopping the AC motor; a controller being connected to the current detecting means, the relay, the relay contact, the selection switch means, the semiconductor switch means, the display means, the run/stop switch means and the setting means, so as to control the relay, the semiconductor switch means and the display means depending on the run or stop selection of the run/stop switch means, the detect current from the current detecting means and the set mode of the selection switch means; and a means for warning an abnormal state in its occurrence.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.